Acid phosphatase activity in human neuronal and glial lipofuscin.

The ultrastructural demonstration of acid phosphatase activity in neuronal and glial lipofuscin of the aged human brain indicates lysosomal activity. Contrary to the constantly high enzyme activity of astroglial lipofuscin and low activity of oligodendroglial lipofuscin, the enzyme activity of neuronal pigment differs in different locations, i.e., in different neuronal populations. The activity is probably based on the importation of lysosomal enzymes into the pigment component of lipofuscin. These facts indicate the possibility of a continuous autophagosomal function of lipofuscin in neuronal and glial cell physiology. Therefore, the findings are arguments against the view that lipofuscin is a wear-and-tear material only and claim for it an active role in cell metabolism.